“Z”‐Type Tilted Quasi‐One‐Dimensional Assembly of Actinide‐Embedded Coinage Metal Near‐Plane Superatoms and Their Optical Properties

Abstract In this work, a novel discovery that the coinage‐metal near‐plane superatoms (CM‐NPSs) formed by embedding actinide elements into the coinage metal rings can realize the “Z”‐type tilted quasi‐one‐dimensional (1D) direct assembly is reported. This success can be attributed to the strong bonding between the overlapping parts of adjacent superatomic motifs. First‐principles calculations reveal that the motifs maintain their geometric and electronic structures robustly during the assembly process. With the accumulation of motifs, the intensity of the absorption peak increases continuously in the ultraviolet‐visible (UV‐Vis) absorption spectra range of 300–450 nm, resulting in the hyperchromic effect, which is closely related to the degree of the participation of Th atoms. Furthermore, the absorption spectra show a continuously tunable feature in the 450–900 nm range, as the interlayer stacking pattern leads to a pronounced redshift. More importantly, the valence 5f‐shells of Th atoms have an increased contribution to the final orbitals of electronic transition, which demonstrates the advantages of the active high angular momentum electrons of actinide elements in spectral properties. These findings provide a valuable reference for the direct artificial assembly of near‐plane superatoms and optical properties of superatomic assemblies embedded with rare elements.

Tables S6-S17. The optimized structural coordinates of (Th@Au 6 ) n (n=1-8). Figure S1. Energy levels of Th@M 6 (M=Au, Ag, Cu). The 1S, 1P and 1D superatomic molecular orbitals (SAMOs) are listed. We found that the bond angles gradually decrease with the change of coinage metal atoms from Au to Cu, which also makes the overall structure gradually appear non-planar. In addition, when the coinage metal atoms change from Au to Cu, the law of Th-M is:

Reference
Th-Ag>Th-Au>Th-Cu, the law of M-M is: Ag-Ag>Au-Au>Cu-Cu. The sum of Th-M covalent radii: Th-Au> Th-Ag> Th-Cu, which does not conform to the bond length laws obtained in this work. The law of the bond lengths is mainly due to the relativistic effect of heavy elements, which is consistent with previous knowledge. [1] Figure S3. The charge density difference (CDD) of Th@M 6 . Red solid lines and blue dashed lines represent the electron aggregation and dissipation. Dark blue, yellow, light blue and orange spheres represent Th, Au, Ag and Cu elements, respectively. The charge density difference (CDD) of three structures were further analyzed. It was found that electrons gathered at the interconnection of each atom, indicating that the atoms were bonded. Figure S4. The energy decomposition analysis (EDA) and redox reaction analysis. (a) The EDA of Th@M 6 and (Th@M 6 ) 2 . For monomers, two selected fragments of EDA are the coinage metal rings and the central atom. For dimers, it is between monomers. Yellow, green and red areas represent the percentage of the electrostatic interaction (E elstat ), orbital interaction (E orb ) and dispersive interaction (E dis ) to the total attractive interaction, respectively. (b) The redox reaction analysis of Th@M 6 . Yellow and green solid lines and dashed lines represent the vertical ionization potential (VIP) and adiabatic ionization potential (AIP), the vertical electron affinity (VEA) and adiabatic electron affinity (AEA), respectively. The red solid line and dashed line represent the ionization potential (IP) and electron affinity (EA) of the coinage metal atoms, respectively.
In order to explore the interactions between the coinage metal rings and the central atom, energy decomposition analysis (EDA) was performed. Two selected fragments for EDA are the coinage metal rings and the central atom. For Th@Au 6 and Th@Cu 6 , the orbital interaction (E orb ) accounts for more than 50% of the total attractive interaction energy, which shows that the E orb is dominant. Therefore, the bonds between the Au 6 and Cu 6 rings and the central atom tend to be covalent. However, for Th@Ag 6 , the electrostatic interaction (E elstat ) is slightly larger than the E orb , the bonds between the Ag 6 ring and Th tend to be ionic. The monomers are divided into two fragments of the dimers. The percentages of E elstat to the total attraction interaction in (Th@Au 6 ) 2 , (Th@Ag 6 ) 2 and (Th@Cu 6 ) 2 are 48.36%, 59.09% and 65.76%, respectively. The results reveal that the interactions between the monomers are dominated by E elstat , indicating that are mainly connected by ionic bond.
We further calculated vertical ionization potential (VIP), adiabatic ionization potential (AIP), vertical electron affinity (VEA) and adiabatic electron affinity (AEA) of three assembled structures. It is found that the law of VIP with the change of the shell atom from Au to Cu is: Th@Au 6 >Th@Cu 6 >Th@Ag 6 , and the law of VEA and AEA is: Th@Au 6 >Th@Ag 6 >Th@Cu 6 . The greater the ionization energy, the less likely it is to lose electrons. The greater the affinity energy, the easier it is to get electrons. It can be seen that Th@Au 6 can easily obtain electrons and exhibit oxidizing properties. Because the geometric configuration is deformed when calculating the AIP, which makes the AIP meaningless, we will not go into too much detail about it in this work.
Previous reports indicate that the law of IP in coinage metal atoms was found to be Au>Cu>Ag [2] , and the law of EA is Au>Ag>Cu [3] . It is preliminarily concluded that when changing the coinage metal atoms of the outer shell, it is the law of the atoms themselves that determines that different. Figure S5. The CDD analysis at five special structures and interaction analyses with the change of ∠Th-Th-Au (marked as α). The structure with α=120° is the most stable structure, α=80° is the face-to-face structure of two monomers, and α=45° is the sub-stable structure. The α=20° and α=145° are the structures with the farther distance between monomers. The red and blue solid lines in CDD indicate electronic aggregation and dissipation, respectively.
To gain insight into the formation mechanism of this "Z"-type offset stacked assembled structure (Th@Au 6 ) 2 , we investigated the interaction and potential energy curve changes during monomer slip process. The change of ∠Th-Th-Au (marked as α) was used to indicate the degree of slippage between monomers. As showed in Figure S5, it can be seen from the potential energy curve that a local minimum appears as α gradually increases to 45°. When the angle gradually increased to 80°, a saddle point appeared, and continued to increase to 120° to reach the lowest point of energy. The binding energy (BE) between monomers at each point is consistent with the conclusion of the potential energy curve. Both confirmed that the structure with the α of 120° is the most stable. Then, five typical structures on the potential energy curve are selected for the CDD analyses. It is found that the charge accumulation area is mainly distributed at the junction of Th and Au between adjacent monomers, resulting in the formation of bonds between the monomers. This indicates that the assembly of monomers mainly involves the charge accumulation between them. To further explore the properties of bonds between monomers, the law of EDA is explored with the changes of α. The results disclose that the value of E elstat is always the largest in the attractive interaction, indicating that the bond between monomers is mainly connected by the ionic bond. But from the most stable structural point of view, monomers assembly occurs when they are balanced by the interaction of attraction and repulsion, which ultimately depends on E int . This has also been explained in previous reports [4] . In the structure of α=120°, E int is the largest, which further proves that the structure is the most stable. This is basically consistent with the results of the potential energy curve and the BE. Figure S6. Trimers and tetramers of Th@Ag 6 and Th@Cu 6 . The left half and right half are trimer and tetramer structures, respectively. Among them, the left side and right side are the initial and final structures, respectively. Th@Cu 6 has two assembly methods. Figure S7. The density of states (DOS) of (Th@Ag 6 ) n and (Th@Cu 6 ) n (n= 1, 2). (a) The DOS of (Th@Ag 6 ) n . (b) The DOS of (Th@Cu 6 ) n . The dotted and solid lines represent the DOS of monomers and dimers, respectively. The diagrams of monomer and dimer highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are given on the right. The position of HOMO and LUMO are displayed and the H-L gap is marked. The purple, blue and pink areas indicate the locations of the SAMOs 1S, 1P and 1D, respectively.
From the density of states (DOS) of Th@Ag 6 and Th@Cu 6 monomers and dimers, it is found that after Th@Cu 6 is assembled into dimers, the trend of DOS and the position of the main peak remain basically unchanged. The position of the main peak has shifted due to the distortion of the Th@Ag 6 dimer structure. It is worth note that both HOMO and LUMO of (Th@Cu 6 ) 2 can form δ symmetry, while the frontier molecular orbitals of (Th@Ag 6 ) 2 cannot be formed, indicating that the structure of (Th@Ag 6 ) 2 is asymmetry. This further proves that Th@Ag 6 did not maintain the electronic properties during the assembly process. Figure S8. The initial and optimized structures of the two-dimensional assembly of (Th@Au 6 ) n (n=2-4).
As shown in Figure S8, our calculated results have presented that the two-dimensional assembly of Th@Au 6 as motifs seems invalid. On the one hand, in the two-dimensional extension process, the interactions of the central Th elements and Au elements are absent, resulting in the inability to support the structure maintaining the two-dimensional state. Thus, the phenomenon of deformation and fusion occurs. On the other hand, since Th@Au 6 itself belongs to near-plane superatom rather than that of pure plane, it is also difficult to maintain the structural properties of the monomers during the two-dimensional assembly process and tends to form aggregate structures. Figure S9. The structural information of (Th@Au 6 ) n (n=1-8). Figure S10. The transition source a-d of (Th@Au 6 ) n (n = 1-8) in the UV-Vis absorption spectra. To visualize the contribution of Th atoms more clearly, the orbitals of the transition sources a-d in the manuscript were scaled up equally. Table S1. Interaction analyses of monomer. The BE and E int between the central atom and the coinage metal rings in the monomer, and average atomization energy (AE) of each atom in the monomer. We only focus on the binding ability between fragments, so BE formula: Atomization energy (AE) formula: The total interaction energy of energy decomposition can be divided into four parts, namely Pauli repulsion, electrostatic interaction, orbital interaction and dispersion interaction: The first term is repulsive interaction, and the last three terms are attractive interaction.
The BE and E int between the central atom and the coinage metal rings in the monomers and the atomization energy (AE) of each atom are calculated. As the shell changes from Au to Cu, the BE between the central atom and coinage metal rings of Th@Au 6 is the largest, and Th@Ag 6 is the lowest. The same result was obtained in the calculation of E int and AE. This shows that compared with other structures, Th@Au 6 is the most stable structure and suitable for assembly.